CVT target engine speed control

ABSTRACT

A machine may include an engine, a traction device, a continuously variable transmission (CVT) connecting the engine to the traction device, an operator input device outputting engine output command signals input by an operator, an engine speed sensor monitoring an engine output speed, and an electronic control module (ECM). The ECM may control the engine to a target engine speed determined from the engine output command signals using engine speed sensor signals as feedback. The ECM determines a CVT transmission ratio that will cause the CVT to apply a load to the engine that will cause the engine to run at the target engine speed.

TECHNICAL FIELD

The present invention relates generally to speed control in vehicles andmachines, and more particularly, to controlling an engine speed andtransmission ratio in a vehicle or machine having a continuouslyvariable transmission by comparing an actual engine speed to a targetengine speed.

BACKGROUND

Transmission systems may be used to couple the output of a prime moveror power source, for example, an internal combustion engine, to a drivenelement or device such as wheels or a work implement on a work machine.Transmissions are typically part of a power train that transmits powerthat may be in the form of torque and/or rotational speed from the powersource to the driven element. A continuously variable transmission (CVT)provides an infinite or continuous range of torque-to-speed outputratios with respect to any given input from the power source. In otherwords, the output of the CVT can be increased or decreased across acontinuous range in infinitesimally small increments.

U.S. Pat. No. 8,216,109 issued on Jul. 10, 2012, to Dahl et al. entitled“Torque-Based Control System for a Continuously Variable Transmission”discloses a method of managing the operation of a machine having anoperator station with one or more operator interface devices, one ormore traction devices and a power train operatively connected to driveat least one of the traction devices. The operator interface devices mayinclude devices for initiating movement of the machine by transmittingsignals to a control module. The power train includes a power source,such as an engine, and a transmission unit connected to receive thepower output from the power source and transmit the power output to thetraction devices. The control module regulates the operation of thetransmission unit in response to one or more inputs from the operatorinterface devices. A first sensor associated with the power sourcesenses an output speed thereof, and a second sensor associated with thetransmission unit and/or the traction device senses a travel speed ofthe machine. The transmission unit may embody a continuously variabletransmission. The control module uses information provided by thesensors to control an output torque of the transmission unit that isdetermined in response to multiple inputs by an operator at the operatorinterface devices.

SUMMARY OF THE DISCLOSURE

In one aspect of the present disclosure, a machine for operating at awork site and traveling over a work surface of the work site isdisclosed. The machine may include an engine, a traction device, acontinuously variable transmission (CVT) operatively connected betweenthe engine and the traction device to transfer power output by theengine to the traction device, an operator input device in an operatorstation of the machine for detecting engine output commands that areinput by an operator of the machine and outputting engine output commandsignals corresponding to the engine output commands input by theoperator at the operator input devices, an engine speed sensorautomatically monitoring an engine output speed of the engine andoutputting engine speed sensor signals corresponding to the engineoutput speed of the engine, and an electronic control module (ECM)operatively connected to the engine, the CVT, the operator input deviceand the engine speed sensor. The ECM is programmed to receive the engineoutput command signals from the operator input device, determine atransmission control target engine speed based on the engine outputcommand signals, determine a transmission ratio for the CVT based on thetransmission control target engine speed to cause the engine to operateat the transmission control target engine speed, and transmittransmission command signals to the CVT to control the CVT so that atransmission output speed divided by a transmission input speed is equalto the transmission ratio determined based on the transmission controltarget engine speed. The ECM is further programmed to receive the enginespeed sensor signals from the engine speed sensor and compare the engineoutput speed from the engine speed sensor signals to the transmissioncontrol target engine speed, and calculate a revised transmission ratiothat will cause the engine output speed to be approximately equal to thetransmission control target engine speed and transmit revisedtransmission command signals to the CVT to control the CVT to therevised transmission ratio in response to determining that the engineoutput speed is not equal to the transmission control target enginespeed.

In another aspect of the present disclosure, a method for controlling anengine output speed of an engine of a machine to be approximately equalto a target engine speed is disclosed. The machine includes a tractiondevice and a continuously variable transmission (CVT) operativelyconnected between the engine and the traction device to transfer poweroutput by the engine to the traction device to propel the machine over awork surface of a work site. The method includes receiving engine outputcommand signals from an operator of the machine indicating a machinefunction commanded by the operator, determining a transmission controltarget engine speed based on the engine output command signals,determining a transmission ratio for the CVT based on the transmissioncontrol target engine speed to cause the engine to operate at thetransmission control target engine speed, and transmitting transmissioncommand signals to the CVT to control the CVT so that a transmissionoutput speed divided by a transmission input speed is equal to thetransmission ratio determined based on the transmission control targetengine speed. The method further includes comparing the engine outputspeed of the engine to the transmission control target engine speed, andcalculating a revised transmission ratio that will cause the engineoutput speed to be approximately equal to the transmission controltarget engine speed and transmitting the revised transmission commandsignals to the CVT to control the CVT to the revised transmission ratioin response to determining that the engine output speed is not equal tothe transmission control target engine speed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an exemplary vehicle or machine that can travelover a work surface;

FIG. 2 is a schematic view of mechanical, electrical and controlcomponents of a power train of the vehicle of FIG. 1;

FIG. 3 is a graph of power versus engine speed with an exemplary lugcurve for an engine of the vehicle of FIG. 1; and

FIG. 4 is a block diagram of a target engine speed control routine inaccordance with the present disclosure that may be executed by anelectronic control module of the vehicle of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary vehicle or machine 10 in the form of a largewheel loader that may traverse a work surface at a work site. While awheel loader is shown, the CVT target engine speed control strategydiscussed herein may be implemented in any other appropriate type ofwork vehicle or machine. The machine 10 includes a frame 12 supporting amachine body 14, and with the frame 12 being supported above the worksurface by traction devices 16. As illustrated, the traction devices 16include a plurality of wheels 16, but the traction devices 16 could beany other appropriate devices such as an undercarriage with tracks,halftracks, or combinations of tracks, wheels or other traction devices.

The machine 10 is driven by a power train including an engine 18operatively connected to a CVT 20 that in turn is operatively connectedto the wheels 16. The CVT 20 transfers power generated by the engine 18to the wheels 16 to rotate the wheels 16 and propel the machine 10 overthe work surface. The CVT 20 may be any automatic transmission that canchange seamlessly through a continuous range of effective gear ratios.For example, the CVT 20 may be a hydrostatic CVT having a variabledisplacement pump pumping hydraulic fluid to either a constantdisplacement or variable displacement hydraulic motor, with the variabledisplacement pump having a swash plate that is adjusted to vary the flowthrough the pump and, correspondingly, the gear ratio of the CVT 20 andthe load on the engine 18. Alternatively, the CVT 20 could be a variablediameter pulley CVT, a toroidal CVT, a cone CVT or the like providingcontinuous adjustment through a range of gear ratios.

An operator can control the movement of the machine 10 along with otheroperations of the machine 10 at an operator station 22. The controlledoperations can include speed control, steering, load dumping, actuationof implements of the machine 10, and the like. The operator station 22may have a plurality of operator input devices 24 for inputting commandsfor the engine 18, the CVT 20 and other systems of the machine 10. Theoperator input devices 24 can include engine throttles, brake pedals,gear shift levers, steering wheels, implement lift and articulationcontrols, graphical user interfaces, and the like. Sensors associatedwith each of the operator input devices 24 detect manipulation of theoperator input devices 24 by an operator and transmit correspondinginput device command signals that are received and processed by anelectronic control module (ECM) 26. Particularly relevant to the presentdisclosure are engine output command signals transmitted from an enginethrottle or the like, or a combination of operator input devices 24 thatmay cause the engine 18 to operate according to conventional enginecontrol strategies, and that may be evaluated by the ECM 26 to determinea target engine speed TES for the engine 18 and a corresponding CVTtransmission ratio TR that will cause the CVT 20 to apply a load to theengine 18 based on a current transmission output speed that will causethe engine 18 to run at the target engine speed TES as the machine 10accelerates, decelerates or maintains speed as commanded by theoperator.

The machine 10 also collects and records operational data relating tothe operation of the machine 10 as it operates within the work site andtraverses the work surface. The machine 10 may include a variety ofsensors 28 operating independently or as components of other control andmonitoring systems to automatically monitor various operational dataduring travel of the machine 10 over the work surface and theperformance of machine operations within the work site. The sensors 28monitoring the operational data may include speed sensors detectingmachine, engine and transmission speeds, and torque sensors sensingtorque at various points along the power train and/or rolling resistanceof the wheels 16. The sensors 28 may also include payload weight sensorsdetecting the weight of a load carried by the machine 10, pressuresensors for suspension cylinder and lift cylinder pressures, and thelike. The operational data monitored by the sensors 28 may also includeroad parameters such as, for example, the grade of the road over whichthe machine 10 is traveling measured by inertial measuring units (IMUs),accelerometers or inclinometers, and the location coordinates andelevation of the machine 10 at a given time as detected by globalpositioning system (GPS) receivers. Some operational data may bemonitored directly, while other data may be derived or calculated fromthe monitored parameters.

The operator input devices 24, the ECM 26 and the sensors 28 arecomponents of a machine control system for the machine 10. Referring toFIG. 2, an exemplary arrangement of mechanical, electrical and controlcomponents of the power train of the machine 10 is shown with thevarious control components integrated into the power train controlsystem. The engine 18 may be configured to receive the engine outputcommands from the operator input devices 24 and operate with thecommanded engine output CEO in response. The engine 18 may beconventional and may include a mechanical governor, an electronicgovernor implemented in software, or other appropriate conventionalengine output control mechanism and control strategy. The engine 18further includes an engine output shaft 30 operatively connected at aninput end of the CVT 20. The engine output shaft 30 may be directlyconnected to the CVT 20, or connected through an intermediate powertransfer device such as a clutch, and torque converter or the like.

The CVT 20 may include a CVT actuator 32 that operates to set or controlthe CVT 20 to achieve a desired ratio of a transmission output speed TOSto a transmission input speed TIS and to create a desired load on theengine 18 through the engine output shaft 30. The configuration of theCVT actuator 32 may vary based on the particular type of CVT 20implemented in the machine 10. For a hydrostatic CVT, the CVT actuator32 may operate to rotate the swash plate of the variable displacementpump and/or a variable displacement motor. The hydrostatic CVT actuator32 may be actuated by the ECM 26 by varying current transmitted to flowcontrol valves of the CVT actuator 32 to move a piston or othercomponent operatively coupled to the swash plate to rotate the swashplate. Variable pulley actuators may control the spacing of sheaves ofpulleys in a variable diameter pulley CVT to vary the gear ratio. TheECM 26 may similarly vary current or other appropriate control signalsto actuate the CVT actuator 32 and vary the spacing of the sheaves. Inalternative embodiments, the CVT actuator 32 may include a CVT actuatorcontroller, and the ECM 26 may transmit appropriate control signals thatare interpreted by the CVT actuator controller that in turn will causethe CVT actuator 32 to actuate and adjust the CVT 20. At the output endof the CVT 20, a transmission output shaft 34 may extend and beoperatively connected to the wheels 16. Similar to the engine outputshaft 30, the transmission output shaft 34 may have intermediatecomponents such as clutches, differentials and the like for transferringthe power output from the CVT 20 to the wheels 16.

The ECM 26 may be capable of processing the information received fromthe operator input devices 24 and the sensors 28 using software storedat the ECM 26, and outputting command and control signals to the engine18 and the CVT actuator 32, and information to displays (not shown) inthe operator station 22. The ECM 26 may include a processor 36 forexecuting a specified program, which controls and monitors variousfunctions associated with the machine 10. The processor 36 may beoperatively connected to a memory 38 that may have a read only memory(ROM) 40 for storing programs, and a random access memory (RAM) 42serving as a working memory area for use in executing a program storedin the ROM 40. Although the processor 36 is shown, it is also possibleand contemplated to use other electronic components such as amicrocontroller, an application specific integrated circuit (ASIC) chip,or any other integrated circuit device. While the discussion providedherein relates to the functionality of a power train control system, theECM 26 may be configured to control other aspects of the operation ofthe machine 10 such as, for example, steering, dumping loads ofmaterial, actuating implements and the like. Moreover, the ECM 26 mayrefer collectively to multiple control and processing devices acrosswhich the functionality of the power train control system and othersystems of the machine 10 may be distributed. For example, the operatorstation 22, the engine 18 and the CVT actuator 32 may each have ECMsthat communicate with the main ECM 26. Such variations in consolidatingand distributing the processing of the ECM 26 as described herein arecontemplated as having use in engine speed control in accordance withthe present disclosure.

The operator input devices 24 are operatively connected to the ECM 26for two-way communications. The operator input devices 24 transmitrequests from the operator generated in response to the operatormanipulating the controls in the operation station 22, and in particularengine commands indicating an engine speed or engine power outputrequested by the operator. The ECM 26 transmits information to beprovided to the operator at output devices (not shown) in the operatorstation 22. The output devices may be any devices capable of providing asensory perceptible output to the operator, such as visual displaydevices, lamps, speakers, and the like. The information communicated tothe operator may include an engine speed, a machine speed, a bucketposition, a load weight, a fuel level, an operational mode indication,and the like.

The sensors 28 may encompass a variety of sensors that are configured tocollect operational data for the machine 10 and transmit sensor signalsto the ECM 26 that correspond to the measured values of the operationaldata. In particular, the sensors 28 discussed herein may collectoperational data that is useful in controlling the speed of the engine18 as the machine 10 travels through the work site. For example, thesensors 28 may include an engine speed sensor 44 and an engine torquesensor 46 operatively coupled to the engine output shaft 30. The enginespeed sensor 44 detects the rotational speed of the engine output shaft30, which corresponds to an engine output speed EOS of the engine 18.The engine torque sensor 46 detects a magnitude of an engine outputtorque EOT created by the engine output shaft 30 and transmitted to theCVT 20. Similarly, a transmission speed sensor 48 and a transmissiontorque sensor 50 are operatively coupled to the transmission outputshaft 34. The transmission speed sensor 48 detects a transmission outputspeed TOS of the transmission output shaft 34, and the transmissiontorque sensor 50 detects a magnitude of a transmission output torque TOTcreated by the transmission output shaft 34 and transmitted to thewheels 16. The engine speed sensor 44 and the transmission speed sensor48 transmit engine speed sensor signals and transmission speed sensorsignals, respectively, to the ECM 26 having values corresponding to theengine output speed EOS and the transmission output speed TOS, while theengine torque sensor 46 and the transmission torque sensor 50 transmitengine torque sensor signals and transmission torque sensor signals,respectively, to the ECM 26 having values corresponding to the engineoutput torque EOT and the transmission output torque TOT.

The performance of the engine 18 may be illustrated graphically in FIG.3. A graph 60 of the power versus the engine speed of the engine 18 hasa lug curve 62 representing the operation of the engine 18 at a constantthrottle amount. For example, the lug curve 62 may represent the 100%throttle engine response. The engine 18 will have a maximum or high idleengine speed at a point 64 where no load is applied to the engine outputshaft 30. As a load on the engine output shaft 30 is increased, thesteady state operating point of the engine 18 will move upward and tothe left on the lug curve 62 decreasing the engine output speed from itscurrent operating point. As the load on the engine output shaft 30 isdecreased, the steady state operating point of the engine 18 will movedownward and to the right on the lug curve 62 increasing the engineoutput speed from its current operating point.

The ECM 26 is operatively connected to the CVT actuator 32 to controlthe load applied by the CVT 20 on the engine 18, and correspondingly theengine output speed EOS, in response to the engine output commandsignals from the operator input devices 24. The operator will indicate adesire to increase, decrease or maintain a power output or output speedof the engine 18 by manipulating the appropriate operator inputdevice(s) 24 in the operator station 22. Appropriate sensors associatedwith the operator input device(s) 24 sense the manipulation of theoperator input device(s) 24 and transmit the engine output commandsignals with values corresponding to the manipulation of the operatorinput device(s) 24. The ECM 26 receives the engine output commandsignals and determines the target engine speed TES and the correspondingtransmission ratio TR based on the commanded engine output CEO.

The ECM 26 may use the engine output commands along with other operatorinputs and/or operational data from the sensors 28 to determine thetarget engine speed TES and the corresponding transmission ratio TR. Thetransmission control software determines the transmission ratio TR forthe CVT 20 needed to apply a load on the engine 18 so that the engine 18will run at the target engine speed TES. The target engine speed TES maybe determined in any appropriate manner based on the engine operatingrequirements for a particular implementation. In one embodiment, thetarget engine speed TES may be a predetermined engine speed stored atthe ECM 26. The target engine speed may be fixed for the machine 10, ormay be updatable via any appropriate mechanism such as operator input atone of the operator input devices 24. In alternative embodiments, thevalue of the target engine speed TES may be mapped to one or moreoperator inputs. For example, the target engine speed TES may bedetermined based on the engine throttle commands from the operator. Thetarget engine speed TES may be proportional to the value of the enginethrottle command so that the target engine speed TES has a maximum valueat the 100% throttle position and decreases as the displacement of theengine throttle decreases. The value of the target engine speed TES maybe similarly affected by additional or alternative operator inputs asnecessary.

The transmission ratio TR may be determined using the target enginespeed TES determined by the ECM 26 along with a current machine speedCMS of the machine 10. In the target engine speed control strategy inaccordance with the present disclosure, the transmission ratio TR may bemanipulated to create a load on the engine 18 at the current machinespeed CMS that will force the engine 18 to operate at the target enginespeed TES. As discussed above, the transmission ratio is equal to thetransmission output speed TOS divided by the transmission input speedTIS. In calculating the transmission ratio TR, the transmission inputspeed TIS may have a value corresponding to the commanded target enginespeed TES. The transmission output speed TOS may be the sensor valuetransmitted by the transmission speed sensor 48, or any otherappropriate value reflecting the current machine speed CMS.

After determining the target engine speed TES and the transmissionration TR, the ECM 26 will cause the CVT actuator 32 to actuate byvarying a control current, transmitting control signals or otherwisecommunicating with the CVT actuator 32. The CVT actuator 32 in responseactuates to cause the CVT 20 to have the CVT ratio to create the load onthe engine 18 that will force the engine output speed EOS to the targetengine speed TES. This process may be repeated over time to maintain theengine output speed EOS approximately equal to the target engine speedTES in implementations where improved engine durability is achievable byoperating in a narrower speed band.

FIG. 4 illustrates a flow diagram for a target engine speed CVTtransmission control routine 100 that may be stored in the memory 38 andexecuted by the ECM 26. The routine 100 is configured so the ECM 26 cancontrol the CVT 20 to maintain the engine output speed EOS approximatelyequal to the target engine speed TES over time using the engine outputspeed signals from the engine speed sensor 44 as feedback. Inalternative implementations, the transmission output speed signals fromthe transmission speed sensor 48 are also used in the control strategy.The control strategy works to drive the engine 18 to the target enginespeed TES by manipulating the transmission ratio TR of the CVT 20.

The routine 100 starts at a block 102 where the ECM 26 receives theengine output commands transmitted from the operator input devices 24and determines the values of the engine output commands input by theoperator to cause the machine 10 to move over the work surface. In someembodiments, the operator input devices 24 may transmit engine outputcommands having values equal to zero if the operator has not operatedany of the operator input devices 24. In these or other embodiments, ifno engine output commands are detected, the ECM 26 may interpret theabsence of engine output commands as an engine output command of zero.When the engine output commands have values of or are determined to beequal to zero, the ECM 26 may maintain the engine 18 at a low idle speedif the machine 10 is not moving, or handle coasting or braking of themachine 10 if the machine 10 is moving over the work surface in thesucceeding steps of the routine 100. It should be noted that the engineoutput commands are concurrently received by the engine 18 and theappropriate conventional engine output control mechanism and controlstrategy will cause the engine 18 to operate at a corresponding enginespeed or engine power.

After the ECM 26 receives the engine output commands at the block 102,control may pass to a block 104 where the ECM may determine atransmission control target engine speed TES corresponding to the valuesin the engine output commands. The ECM 26 may determine the targetengine speed TES using any appropriate method such as those describedabove. Subsequent to the determination of the target engine speed TES,control may pass to a block 106 where the ECM 26 may calculate thetransmission ratio TR for the CVT 20 that will apply a load to theengine 18 to force the engine 18 to run at approximately the targetengine speed TES determined at the block 104. The ECM 26 may determinethe transmission ratio TR using any appropriate method such as thosedescribed above.

After determining the target engine speed TES and the transmission ratioTR at the blocks 104, 106, respectively, control passes to a block 108where the ECM 26 transmits transmission command signals to the CVTactuator 32. Upon receiving the transmission command signals, the CVTactuator 32 adjusts the CVT 20 to provide the calculated transmissionratio TR between the transmission output shaft 34 and the engine outputshaft 30. With the CVT 20 creating the transmission ratio TR between theshafts 30, 34, the CVT 20 creates the load on the engine 18 to force theengine 18 to the target engine speed TES. The transmission commandsignals may be the appropriate type of input signals for the particularCVT actuator 32 implemented in the machine 10, such as varying currents,digital control signals or other appropriate control signals such asthose described above.

With the CVT actuator 32 controlling the CVT 20 per the transmissioncommand signals from the ECM 26 to force the engine 18 toward the targetengine speed TES, control may pass to a block 110 where the ECM 26compares the desired engine speed (i.e., target engine speed TES) to theactual engine speed (i.e., engine output speed EOS). By utilizing theengine output speed EOS as the feedback signal, the engine 18 may bemaintained at approximately the target engine speed TES to reduce wearon the engine 18 that can be caused by highly fluctuating engine speeds.After the comparison, control may pass to a block 112 where the ECM 26evaluates whether the engine output speed EOS is too low. In someimplementations, any variation in the engine output speed EOS from thetarget engine speed TES may cause corrective action to be taken to bringthe engine output speed EOS back to the target engine speed TES. Inother implementations, the difference may be required to be greater thana predetermined minimum engine speed error for corrective action tooccur. For example, the difference between the engine output speed EOSand the target engine speed TES may be required to be greater than aspecified number of revolutions per minute or a specified percentage ofthe target engine speed TES for corrective action to occur.

If the ECM 26 determines at the block 112 that the engine output speedEOS is less than the target engine speed TES by more than a minimumengine speed difference, control may pass to a block 114 where the ECM26 may calculate a revised transmission ratio TR that will increase theengine output speed EOS. As shown in the graph 60 of FIG. 3, the enginespeed increases as the load on the engine output shaft 30 decreases.Consequently, the ECM 26 will determine a reduced transmission ratio TRthat will reduce the load on the engine output shaft 30 and allow theengine output speed EOS to increase for the same throttle setting of theengine 18. For a hydrostatic CVT, the reduced transmission ratio TR mayequate to rotating the swash plate of the variable displacement pumptoward a zero flow or neutral position so that the fluid displacementper revolution of the pump input shaft is reduced. For a variablediameter pulley CVT, an input pulley diameter may be decreased and anoutput pulley diameter correspondingly increased to increase the numberof rotations of the input pulley per rotation of the output pulley.Similar adjustments will be determined by the ECM 26 for other types ofCVTs 20. After the ECM 26 determines the reduced transmission ratio TRat the block 114, control may pass back to the block 108 to outputupdated transmission command signals to the CVT actuator 32 to adjustthe transmission ratio TR of the CVT 20.

If the engine output speed EOS is not too slow at the block 112, controlpasses to a block 116 where the ECM 26 determines whether the engineoutput speed EOS is too fast. As discussed above, in variousimplementations, corrective action may be taken any time the engineoutput speed EOS is greater than the target engine speed TES to reducethe engine output speed EOS, or corrective action may be taken if theengine output speed EOS is greater than the target engine speed TES by apredetermined number of revolutions per minute or percentage above thetarget engine speed TES. If the ECM 26 determines that the engine outputspeed EOS is greater than the target engine speed TES by more than aminimum engine speed difference, control may pass to a block 118 wherethe ECM 26 calculates a revised transmission ratio TR that will reducethe engine output speed EOS. Per the graph 60 of FIG. 3, increasing theload on the engine output shaft 30 will reduce the engine output speedEOS. The load on the engine 18 can be increased by increasing thetransmission ratio TR. In a hydrostatic CVT, the swash plate to thevariable displacement pump can be rotated to increase the fluid flowthrough the pump. For a variable diameter pulley CVT, the input pulleydiameter can be increased and the output pulley diameter can becorrespondingly decreased to decrease the number of rotations of theinput pulley per rotation of the output pulley. Other CVTs 20 can beadjusted as necessary to increase the transmission ratio TR. After theECM 26 determines the increased transmission ratio TR to slow down theengine 18 to the target engine speed TES, control may pass back to theblock 108 to transmit the updated transmission command signals to theCVT actuator 32.

If the ECM 26 determines that the engine output speed EOS is equal tothe target engine speed TES, or differs within an acceptable range fromthe target engine speed TES, at the blocks 112, 116, control may passback to the block 102 to continue receiving and evaluating the engineoutput commands from the operator input devices 24.

In the preceding discussion, the engine output speed EOS is impliedlythe control error for the target engine speed control routine 100.Consequently, the engine output speed EOS is directly compared to thetarget engine speed TES to determine whether the transmission ratio TRmust be updated to get the engine output speed EOS within an acceptablerange about the target engine speed TES. In alternative implementations,the transmission ratio TR can be used as the control error since thetransmission ratio TR is being adjusted to correct errors in the engineoutput speed EOS. In such implementations, the routine 100 may beadjusted to evaluate an actual transmission ratio ATR of the CVT 20relative to a desired transmission ratio DTR to determine whether toadjust the transmission ratio TR. In the modified routine 100, thedesired transmission ratio DTR may be equal to the transmission outputspeed TOS measured by the transmission speed sensor 48 divided by thetarget engine speed TES determined by the ECM 26. The actualtransmission ratio ATR is equal to the transmission output speed TOSdivided by the engine output speed measured by the engine speed sensor44.

In this implementation, the routine 100 begins at the blocks 102, 104,106, 108 as described above. At the block 110, the ECM 26 calculates andcompares the desired transmission ratio DTR to the actual transmissionratio ATR instead of directly comparing the engine output speed EOS tothe target engine speed TES. Control then passes to the block 112 todetermine whether the actual transmission ratio ATR is greater than thedesired transmission ratio DTR (i.e., the engine output speed EOS isless than the target engine speed TES, and therefore too slow). If theactual transmission ratio ATR is too high, the engine output speed EOSmust be increased to reduce the actual transmission ratio ATR.Consequently, if the actual transmission ratio ATR is greater than thedesired transmission ratio DTR by a predetermined minimum transmissionratio error, control passes to the block 114 for the ECM 26 to determinea reduced transmission ratio TR that will increase the engine outputspeed EOS and thereby reduce the actual transmission ratio ATR.

If the actual transmission ratio ATR is not greater than the desiredtransmission ratio DTR at the block 112, control passes to the block 116to determine whether the actual transmission ratio ATR is less than thedesired transmission ratio DTR (i.e., the engine output speed is greaterthan the target engine speed TES, and therefore too fast). If the actualtransmission ratio ATR is too low, the engine output speed EOS must bedecreased to increase the actual transmission ratio ATR. If the actualtransmission ratio ATR is too low by more than the predetermined minimumtransmission ratio error, control passes to the block 118 for the ECM 26to determine an increased transmission ratio TR that will decrease theengine output speed EOS and increase the actual transmission ratio ATR.

INDUSTRIAL APPLICABILITY

The method for target engine speed control in accordance with thepresent disclosure utilizes the speed of the engine 18, either directlyor indirectly via the actual transmission ratio TR, to maintain theengine output speed EOS approximately equal to the target engine speedTES determined based on engine output commands from an operator.Previous control strategies utilize the transmission output speed TOS orthe transmission output torque to control cause the machine 10 torespond to the operator's desired machine output. Such controlstrategies provide good resolution on the output torque or the machinespeed in comparison to the operator commands. However, the engine speedfluctuates to accommodate changing driveline efficiencies in the powertrain. In some situations, high fluctuations in engine speeds can causegreater wear in the engine 18 over time. In some implementations,maintaining the engine 18 at as constant an engine speed as possible fordurability and to prolong the life of the engine 18 may be a higherpriority machine requirement than precise control of the speed or torqueat the output of the CVT 20. The control strategy in accordance with thepresent disclosure provides good resolution on the engine speed whileallowing the transmission output speed TOS and the output torque tofluctuate to accommodate the changing driveline efficiencies in thepower train.

While the preceding text sets forth a detailed description of numerousdifferent embodiments, it should be understood that the legal scope ofprotection is defined by the words of the claims set forth at the end ofthis patent. The detailed description is to be construed as exemplaryonly and does not describe every possible embodiment since describingevery possible embodiment would be impractical, if not impossible.Numerous alternative embodiments could be implemented, using eithercurrent technology or technology developed after the filing date of thispatent, which would still fall within the scope of the claims definingthe scope of protection.

It should also be understood that, unless a term was expressly definedherein, there is no intent to limit the meaning of that term, eitherexpressly or by implication, beyond its plain or ordinary meaning, andsuch term should not be interpreted to be limited in scope based on anystatement made in any section of this patent (other than the language ofthe claims). To the extent that any term recited in the claims at theend of this patent is referred to herein in a manner consistent with asingle meaning, that is done for sake of clarity only so as to notconfuse the reader, and it is not intended that such claim term belimited, by implication or otherwise, to that single meaning.

What is claimed is:
 1. A machine for operating at a work site andtraveling over a work surface of the work site, the machine comprising:an engine; a traction device; a continuously variable transmission (CVT)operatively connected between the engine and the traction device totransfer power output by the engine to the traction device; an operatorinput device in an operator station of the machine for detecting engineoutput commands that are input by an operator of the machine andoutputting engine output command signals corresponding to the engineoutput commands input by the operator at the operator input device; anengine speed sensor automatically monitoring an engine output speed ofthe engine and outputting engine speed sensor signals corresponding tothe engine output speed of the engine; and an electronic control module(ECM) operatively connected to the engine, the CVT, the operator inputdevice and the engine speed sensor, wherein the ECM is programmed to:receive the engine output command signals from the operator inputdevice, determine a transmission control target engine speed based onthe engine output command signals, determine a transmission ratio forthe CVT based on the transmission control target engine speed to causethe engine to operate at the transmission control target engine speed,transmit transmission command signals to the CVT to control the CVT sothat a transmission output speed divided by a transmission input speedis equal to the transmission ratio determined based on the transmissioncontrol target engine speed, receive the engine speed sensor signalsfrom the engine speed sensor and compare the engine output speed fromthe engine speed sensor signals to the transmission control targetengine speed, and calculate a revised transmission ratio that will causethe engine output speed to be approximately equal to the transmissioncontrol target engine speed and transmit revised transmission commandsignals to the CVT to control the CVT to the revised transmission ratioin response to determining that the engine output speed is not equal tothe transmission control target engine speed.
 2. The machine of claim 1,wherein the ECM is programmed to determine the transmission controltarget engine speed based on a manipulation of an engine throttle. 3.The machine of claim 1, wherein the CVT comprises a CVT actuatoroperatively connected to the ECM, wherein the CVT actuator receives thetransmission command signals and causes the CVT to be set to thetransmission ratio determined by the ECM.
 4. The machine of claim 1,wherein the ECM is programmed to calculate the revised transmissionratio to be less than the transmission ratio in response to determiningthat the engine output speed is less than the transmission controltarget engine speed.
 5. The machine of claim 1, wherein the ECM isprogrammed to calculate the revised transmission ratio to be greaterthan the transmission ratio in response to determining that the engineoutput speed is greater than the transmission control target enginespeed.
 6. The machine of claim 1, comprising a transmission speed sensoroperatively connected to the CVT and the ECM and automaticallymonitoring the transmission output speed of the CVT and outputtingtransmission speed sensor signals corresponding to the transmissionoutput speed of the CVT, wherein the ECM is programmed to calculate adesired transmission ratio that is equal to the transmission outputspeed divided by the transmission control target engine speed, andcalculate an actual transmission ratio that is equal to the transmissionoutput speed divided by the engine output speed.
 7. The machine of claim6, wherein the ECM is programmed to calculate the revised transmissionratio to be less than the transmission ratio in response to determiningthat the actual transmission ratio is greater than the desiredtransmission ratio.
 8. The machine of claim 6, wherein the ECM isprogrammed to calculate the revised transmission ratio to be less thanthe transmission ratio in response to determining that the actualtransmission ratio is greater than the desired transmission ratio bymore than a predetermined minimum transmission ratio error.
 9. Themachine of claim 6, wherein the ECM is programmed to calculate therevised transmission ratio to be greater than the transmission ratio inresponse to determining that the actual transmission ratio is less thanthe desired transmission ratio.
 10. The machine of claim 6, wherein theECM is programmed to calculate the revised transmission ratio to begreater than the transmission ratio in response to determining that theactual transmission ratio is less than the desired transmission ratio bymore than a predetermined minimum transmission ratio error.
 11. A methodfor controlling an engine output speed of an engine of a machine to beapproximately equal to a target engine speed, wherein the machineincludes a traction device and a continuously variable transmission(CVT) operatively connected between the engine and the traction deviceto transfer power output by the engine to the traction device to propelthe machine over a work surface of a work site, the method comprising:receiving engine output command signals from an operator of the machineindicating a machine function commanded by the operator; determining atransmission control target engine speed based on the engine outputcommand signals; determining a transmission ratio for the CVT based onthe transmission control target engine speed to cause the engine tooperate at the transmission control target engine speed; transmittingtransmission command signals to the CVT to control the CVT so that atransmission output speed divided by a transmission input speed is equalto the transmission ratio determined based on the transmission controltarget engine speed; comparing the engine output speed of the engine tothe transmission control target engine speed; and calculating a revisedtransmission ratio that will cause the engine output speed to beapproximately equal to the transmission control target engine speed andtransmitting revised transmission command signals to the CVT to controlthe CVT to the revised transmission ratio in response to determiningthat the engine output speed is not equal to the transmission controltarget engine speed.
 12. The method of claim 11, comprising calculatingthe revised transmission ratio to be less than the transmission ratio inresponse to determining that the engine output speed is less than thetransmission control target engine speed.
 13. The method of claim 11,comprising calculating the revised transmission ratio to be less thanthe transmission ratio in response to determining that the engine outputspeed is less than the transmission control target engine speed by morethan a predetermined minimum engine speed error.
 14. The method of claim11, comprising calculating the revised transmission ratio to be greaterthan the transmission ratio in response to determining that the engineoutput speed is greater than the transmission control target enginespeed.
 15. The method of claim 11, comprising calculating the revisedtransmission ratio to be greater than the transmission ratio in responseto determining that the engine output speed is greater than thetransmission control target engine speed by more than a predeterminedminimum engine speed error.
 16. The method of claim 11, comprisingcalculating a desired transmission ratio that is equal to thetransmission output speed divided by the transmission control targetengine speed, and calculating an actual transmission ratio that is equalto the transmission output speed divided by the engine output speed. 17.The method of claim 16, comprising calculating the revised transmissionratio to be less than the transmission ratio in response to determiningthat the actual transmission ratio is greater than the desiredtransmission ratio.
 18. The method of claim 16, comprising calculatingthe revised transmission ratio to be less than the transmission ratio inresponse to determining that the actual transmission ratio is greaterthan the desired transmission ratio by more than a predetermined minimumtransmission ratio error.
 19. The method of claim 16, comprisingcalculating the revised transmission ratio to be greater than thetransmission ratio in response to determining that the actualtransmission ratio is less than the desired transmission ratio.
 20. Themethod of claim 16, comprising calculating the revised transmissionratio to be greater than the transmission ratio in response todetermining that the actual transmission ratio is less than the desiredtransmission ratio by more than a predetermined minimum transmissionratio error.